VENTILATED FAÇADE: A VALUABLE STUDY
The Universitat Autònoma de Barcelona’s Department of Chemistry buildings provide the perfect setting for a thermographic study on thermal comfort and energy efficiency performance comparing a ventilated façade with one made of concrete.
Hosted within the Department of Science complex, the Department of Chemistry occupies two interconnecting buildings in the Universitat Autònoma de Barcelona’s Bellaterra campus. Built in the late 1960’s, these two box-like buildings are among the oldest structures on the university grounds. While one has a painted concrete exterior, the other was renovated and displays a ventilated façade.
“ This setting allows us to include in just one thermographic image the behaviour of a
traditional façade next to one clad with Trespa® Meteon®.”
Xavier Viola i González, director of Efcore and thermographer
One of the buildings underwent a major refurbishment in 1992, as it needed to accommodate new laboratories and a high concentration of equipment. Because Spain already had in place its first norms on the thermal regulation of buildings, it was decided that a ventilated façade was the best solution to refurbish the building made of precast concrete. Trespa® Meteon® panels in Mid Grey were chosen as cladding.
More than 20 years later, the Department’s facilities is providing the perfect setting for a thermographic study on thermal comfort, condensation and energy efficiency performance with and without a ventilated façade. “We have the phrase ‘an image is worth a thousand words,’ well this setting allows us to include in just one thermographic image the behaviour of a traditional façade next to one clad with Trespa® Meteon®,” says Xavier Viola i González, director of Efcore, the Spanish firm in charge of the study.
The two buildings of the Department of Chemistry at the UAB’s Bellaterra campus. On the left is the renovated structure with Trespa® Meteon®, to the right the one still in its original state.
Defined by a typical 1960’s architectural style, the five-storey buildings were built with precast concrete sandwich wall panels with no insulation. They both use a central heating system during winter months. Apart from the façade, the two constructions have the same if not almost identical characteristics in terms of geographical orientation, interior conditions, use, height, occupancy, maintenance service, management and end users. These elements are the ones that could distort the results of a comparative study. Also, there were no adjacent nor nearby buildings that could influence the measurements.
“We couldn’t have found better conditions to do the thermographic study, because all the characteristics were the same with the exception of the ventilated façade, which was the object of the study,” explains Viola i González. After an initial analysis of the emissivity of the façade materials,
which guaranteed the reliability of the images, Efcore took a series of thermal images in February 2014, and a second set in July of the same year. This allowed Viola i González and technical architect Josep Lluís Escobedo i Parés to analyse the behaviour of both buildings during winter and summer.
According to the thermographic images, during summer months, the temperature of the concrete façade’s exterior surface is very close to the outside temperature. The opposite happens during winter, where the concrete surface temperature is higher than the outside temperature. Without insulation, heat goes from indoor to outdoor instead of remaining inside. Additionally, there are notable temperature variations internally. These findings indicate “a greater heat transfer from the exterior to the interior, and an important energy loss through the concrete façade,” reads the report. In turn, these losses and transfers resulted into higher energy costs to cool and heat the building, while providing greater discomfort to its users, who feel the temperature fluctuations.
The situation is quite different for the refurbished building. The temperature of Trespa® Meteon® surface tends to be higher during hotter months while it is very similar to the outside temperature during winter. No cold interiors were noted, and minimum energy losses from the interior to the exterior were reported. These results are linked to the existence of a ventilated façade system, which includes insulation and an air cavity that provides a continuous airflow that aids the removal of heat and moisture.
“The Trespa® Meteon® panels and the air cavity protect the insulation that, in turn, protects the rest of the envelope, improving the overall thermal performance,” notes the independent study. Because the internal temperature is more even, the comfort is
greater. In addition, less energy is needed to cool the building during summer or to heat it during the cold months. According to Efcore calculations, there is around a 22% of energy savings when compared to the energy consumption before renovation.
For the refurbishment of the Department of Chemistry, Trespa® Meteon® panels with a thickness of 8 mm were used. The ventilated façade has an air cavity of 30 mm and between 20 and 30 mm of insulation, which was compliant with then valid Spanish construction codes that had introduced an insulation of 20-25 mm minimum thickness.
“The ventilated façade of the Department of Chemistry was already ahead of the local requirements, as the insulation was installed on the exterior walls. This already minimized the thermal bridges,” says Viola i González. “Obviously, had the insulation been between 80 and 100 mm, as its specified now, the energy savings and the reduction of CO2 emissions would be higher.”